Typing sheet for thermal duplicating processes

ABSTRACT

An improved image control means comprising a typing sheet particularly adapted for use in a thermal duplicating process. The typing surface of the sheet is formed by a substantially uniform mixture of oil receptive particles and oil resistive particles. The typing sheet has a thickness not in excess of about 2.5 mils and is used in conjunction with a backing sheet having a thickness of at least about 2 mils.

I United States Patent 1191 1111 3,9 Sund 1 51 Dec. 16, 1975 15 TYPINGSHEET FOR THERMAL 2.790,742 4/1957 Wharton 161/269 DUPLICATING PROCESSES2,934,467 4/1960 Bergstein 161/268 3,592,725 7/1971 Yoshimura 161/249lnventofl Joseph Sund, L08 Aflgeles, 3,745,038 7/1973 Jeffs 117/1388 ECalif. 3,776,755 12/1973 Paulson 161/406 [73] Assignee: Bell & HowellCo., Chicago, Ill.

Primary ExaminerGeorge F. Lesmes [22] Ffled' 1973 AssistantExaminerEllis P. Robinson [21] Appl' No.: 409,529 Attorney, Agent, orFirm-Nilsson, Robbins, Bissell,

Dalgarn & Berliner [52] US. Cl. 428/325; 101/470; 428/337;

428/536; 428/330 [57] ABS CT [51] Int. Cl. B3213 5/16; B32B 19/04 Animproved image control means comprising a typ- Field of Search 406 ingsheet particularly adapted for use in a thermal dul6l/406, 268, 247,DIg. 5, 249, 265; plicating process. The typing surface of the sheet isformed by a substantially uniform mixture of oil re- 38-8 28/325, 337,339, 537, 507, 500, ceptive particles and oil resistive particles. Thetyping 330 sheet has a thickness not in excess of about 2.5 mils and isused in conjunction with a backing sheet having [56] References Cited athickness of at least about 2 mils.

UNITED STATES PATENTS 8 C 3 D 0 F 2,778,301 1/1957 Brinnick 101/462rawmg gums US. Patent Dec. 16, 1975 3,927,237

HG/MEN T A FIG.2.

P/GME/VT L) FIGS.

TYPING SHEET FOR THERMAL DUPLICATING PROCESSES FIELD OF THE INVENTIONThe present invention generally relates to image duplicating and moreparticularly to thermal duplicating processes and improved image controlmeans for use therein.

BACKGROUND AND SUMMARY OF THE INVENTION Various types of thermalduplicating processes, that is, processes which involve the thermaltransfer of heatsensitive material, are well known in the art. See, forexample, those processes described in US. Pat. Nos. 3,122,997 and3,122,998 issued to Raczynski et al., as well as US. Pat. Nos.1,514,677, 2,501,495, 2,611,313, 2,808,777, 2,939,009, 3,109,748,3,181,965, 3,260,603, 3,262,386, 3,267,848, 3,283,708, 3,293,055,3,304,015, 3,384,015 and 3,706,276.

In the typical thermal duplicating process,,an original is typed onconventional typing paper with a typewriter or the like. This typedoriginal is then duplicated by placing it in an assembly with a transfersheet substrate carrying a fusible layer of heat sensitive material andan image-receiving sheet which has its receiving surface in contact withthe fusible layer. Since the typing ink which is used to fonn the typedimage on the original is infrared absorptive, the areas on the originalwhich bear the typed image absorb more infrared radiation than do theimage-free areas of the original. Exposure radiation in the infraredregion is converted to thermal energy in the original so that the imagedareas of the original acquire a higher thermal energy content that theimage-free areas, and provide a thermal pattern corresponding to thevisible image pattern. The thermal pattern is conducted through thesubstrate of the transfer sheet to the heat sensitive layer toselectively fuse the fusible material thereof in a pattern correspondingto the visible image. The fused material is transferred to theimage-receiving sheet, which then serves as the desired duplicate or isused as a master in a solvent duplicating or lithographic printingprocess.

In spirit duplicating systems, the heat-sensitive layer contains waxes,.or the like fusible material, mixed with an alcohol-soluble dye toproduce the image color in the ultimate copy. The waxy material isthermally transferred to the image-receiving, master sheet after whichthe master is placed on a drum and contacted successively with sheets ofcopy paper wet with volatile alcohol solvent for the dye. The solventdissolves part of the dye in the master image and transfers it to thecopy sheet.

In a second type of spirit duplicating process, the transferred imagematerial contains a chemical reagent which reacts with a second reagentin the copy sheet to form the visible image. In offset lithographicprinting, the imagereceiving sheet serves as a printing plate. Each suchprocess depends on thermal image transfer at some stage in order to forma master from which copies can be made.

Although thermal image transfer processes usually are relativelyinexpensive and effective, they generally yield images of poorresolution. This is also true with impact master duplicating systems.The latter systems employ a special typing sheet which becomes themaster when typed upon. Any mishap in the duplication process whichdestroys or damages the master necessitates completely retyping theimpact master. Furthermore, storage of the original for future use isinconvenient since the dye transfer tendency of such masters requiresthat special storage drawers be used so that the masters can be isolatedfrom other documents. This is not the case with thermal duplicatingprocesses, since the original is not utilized as the duplicating master.

Despite the advantages of thermal duplicating processes over impactmaster duplicating processes, the latter are more frequently used,possibly because of the slightly better image resolution of the latter.In this regard, thermal duplicating processes provide copies whichexhibit more non-uniformity in the depth, clarity and completeness oftype characters, so that in some cases only the hollow outlines of thecharacters are seen. Moreover, edge sharpness of the characters is lessso that overall image appearance has less contrast.

One reason for the inferior quality of thethermally transferred image isthe poor quality of the original image for thermal copying purposes.While the typed image on the original typing paper may appear on thenaked eye to be sharp and uniform, such image may be incapable of beingaccurately duplicated by the thermal process. In this regard, mostoriginal typing papers are uncoated and have surfaces roughly structuredby randomly distributed paper fibers. A typed image on such a surfacedoes not make even and smooth contact with the back of the transfersheet, thus adversely affecting the flow of the heat pattern and thevisible pattern formed therefrom. Moreover, during typing the impact ofthe typing keys on the original paper causes indentation of the paper.During thermal imaging, the indented image-bearing area of the originalcannot make direct contact with the transfer sheet, so that there is avoid or air gap therebetween. This also impedes transfer of the thermalpattern and may distort the pattern.

A further reason for inadequate image duplication in thermal duplicatingprocesses is the lack of uniformity of filling of the typed characterson the original typing paper. The typing ink does not wet the paperfibers of the original typing paper well enough to stick uni formly.Instead, the ink tends to collect in the crevices formed by theinterstices of the paper fibers. Accordingly, the heat pattern generatedfrom the typed char acters of the original sheet is uneven and hasunsharp edges.

A still further, more recent, reason for inadequate thermal imageduplication is the commonplace use of plastic typing ribbons, such asthose formed of Mylar, wherein a combination of dye and wax is used inplace of ink. Such images tend to transfer to the back of the masterduring thermal duplication processes.

The present invention solves the described problems encountered byconventional thermal duplicating processes by providing a typed originalwhich features uniformly inked typed characters with sharp edgedefinition and absence of indentations in the areaof the typedcharacters. When a Mylar type ribbon is used, the image is anchored andsecured in original position. The type characters are broken up into alarge number of sub-units which exhibit a greater heat loss than largesolid typed areas, and therefore require a greater exposure time toinfrared radiation to provide the desired thermal pattern. However,since the sub-units are all small and there is no large solid area inthe original typed sheet, regardless of the size and shape of the typedcharacters, all image areas can be given the same exposure to infraredradiation in order to produce uniform and sharp thermal images andsubsequent sharp and uniform duplicated visible images.

In accordance with the present invention an original typing sheet isprovided which has a typing surface formed by a substantially uniformmixture of oil receptive particles and oil resistive particles. Thus,the typing surface is divided into small regions which are alternatelyoil receptive and non-receptive (oil resistive). Moreover, the typingsheet is thin (not in excess of about 2.5 mils) and compliant and backedin use with a movable smooth backing sheet of at least 2.0 mils inthickness, so that when it is typed upon, no appreciable indentingoccurs. Instead, energy transmitted to the typing sheet upon impactthereof by the typing keys is transferred to and absorbed by the backingsheet.

As a result of the described surface division, ink and dye-waxcombinations are strongly anchored to the oil receptive .particlesresulting in a reticulation of the image and retention of the image onthe typing sheet during thermal processing. Image spread is markedlydecreased as a result of heat dissipation through the oil resistiveregions. The result is a typed original which retains its relativelysmooth highly uniform surface while providing inked characters forming avisible pattern which can be more accurately thermally transferred. Theresulting thermal transfer copies are clearer, sharper and of higheroverall quality than heretofore obtained by thermal duplication.

The improvement in duplicating processes, provided through the use ofthe novelon'ginal typing sheet and backing sheet combination, can beeffected inexpensively and without additional processing steps.Moreover, the novel original typing sheet and backing sheet can bereadily fabricated of conventional materials. Further advantages are setforth in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged schematiccross-section of an embodiment of the improved image control means ofthe invention; I

FIG. 2 is an idealized schematic view of one type of surface of a typingsheet utilized in the embodiment of FIG. 1, taken on the line 2--2 ofFIG. 1; and

FIG. 3 is an idealized schematic view of the surface of a second type ofsurface of a typing sheet which can be utilized in the embodiment ofFIG. 1.

DETAILED DESCRIPTION The present invention is most advantageouslyutilized in conjunction with a backing sheet and with certain thicknessparameters. Referring to FIG. 1, the typing sheet is one component of acontrol means comprising an original typing sheet 12 which includes apaper base sheet 14 having a coating 16 on one surface thereof whichpreferably is calendered. The coating 16 forms the typing surface 18 ofthe sheet 12. The control means 10 also includes a backing sheet 20which removably abuts the surface 22 of the sheet 12 on the sideopposite to that which bears the coating 16.

The typing sheet 12 should be not in excess of about 2.5 mils inthickness and should be compliant, that is, resilient and flexible, sothat energy imparted thereto upon impact of a typing key on the surface18 will not permanently deform the same but will be transmitted readilytherethrough and be absorbed and dissipatedby 4 the backing sheet 20.The thinner the sheet 12, within practical limits of resistance tocutting by typing keys and handling without damage, the more efficientwill be the energy transfer.

It will be noted that the base sheet 14 can be fabricated of anycellulosic fibrous material so as to be of sufficient strength,compliance and thickness. Usually, relatively thin typing paper or thelike will be satisfactory. Tissue typing paper is one suitable example.Others include capacitor paper and Onion skin paper. Usually, the base14 will have a thickness of between about 1 and about 1.5 mils, with thecoating 16 comprising the remaining thickness of the sheet 12.

The coating 16 is generally from about 0.1 to about 0.4 mils inthickness and comprises a particulate mixture of inorganic pigments orwhiteners in a dry adhesive binder. Specifically, the particulatemixture comprises a substantially uniform mixture of oil receptiveparticles (A) and oil resistive particles (B) in a volume ratio of ABabout 0.5:] to about 8:1.

The term oil receptive is meant to define particles having an oilabsorption of at least 30 weight percent. The term oil resistive ismeant to define particles having an oil absorption of less than 20weight percent. It will be appreciated that many materials will be oilreceptive or oil resistive depending upon a number of physical factorssuch as particle size, method of formation, heat treatment if any, etc.Since a particular material can be either oil receptive or oilresistive, designation of that material as one or the other is meant torefer to the compound in such physical state, as known to the art, as tohave that property. In this regard, for any particular materiaL'thesmaller the particle size the greater will be its capacity to absorboil. Therefore, in the practice of the present invention, it is found tobe desirable to use as oil receptive particles inorganic salts andoxides having a diameter of about less than 4 microns, preferably in therange of about 0.1 micron to about 4 microns, and to use as oilresistive particles inorganic salts and oxides having a diameter of atleast 8 microns, preferably in the range of about 8 microns to about I00microns.

Subject to the foregoing criteria, the inorganic particulate materialused in the coating 16 includes such inorganic salts and/or inorganicoxides as, for example, glass beads, clays, such as calcite clay, kaolinor attapulgite, bentonite, hydrated aluminum silicate, silica, magnesia,titania, alumina, calcium carbonate, magnesium carbonate and the like. Asuitable mixture of such components can be mixed with a powdered orliquid adhesive binder, such as a water-soluble or organicsolvent-soluble resin, for example, acrylic emulsion, polyvinyl acetate,starch, polyester resin, alkyd resins, polystyrene,melamine-formaldehyde, urea-formaldehyde, polyvinyl chloride or thelike, in a suitable solvent.

The coating formulation, as specifically illustrated by the Examplesherinafter, can be obtained by simple mixture of the particles indesired ratio in the chosen binder and solvent. The coating can beformed'by applying the formulation in the wet state on a tissue paper(1.5 mil thickness) base sheet. so as to form a layer about 0.3 milthick after drying and calendering. The coating is calendered, e.g.,with a smooth steel face roller at 1000 pounds per square inch to obtaina coating having the desired distribution of oil receptive andoilrejective regions. V

Referring to FIG. 2, there is illustrated, in idealized schematicfashion, the surface coating 16 of the sheet prepared with a 3:1 ratioof oil receptive particles 24 to oil resistive particles 26. Referringto FIG. 3, there is similarly illustrated the surface coating 16' of asheet prepared with a 1:1 ratio of oil receptive particles 24' to oilresistive particles 26'. The result in each case is a surface divisioninto alternate oil receptive and oil resistive regions. As a result,ink, dye-wax combinations and the like become strongly anchored to theoil receptive particles A while not adhering to the oil resistiveparticles B resulting in a reticulation of the image and breaking-up ofthe image into small parts, albeit the image, to the eye, appearsuniform. As a further result, when thermally processed, heat dissipationthrough the B particle regions prevents image spread.

Referring again to FIG. 1, the second component of the novel imagecontrol means comprises the backing sheet 20. The sheet 20 issufficiently smooth, at least at its surface abutting the typing sheet,so as to closely contact the typing sheet and thus readily receive andabsorb the typing key impact force transmitted thereto through thetyping sheet. While any suitable material can be used, it has been foundthat resilient polyethylene terephthalate sheet material is particularlysuitable. Such sheet material must be sufficiently thick yet resilientso as to readily absorb and dissipate the energy transmitted thereto. Ithas been found that sheets of at least 2 mils thickness are required inorder to provide the proper energy absorption. Suitable examples ofmaterials for use as the sheets 20 and 28 are as follows: Mylar (apolyethylene teraphthalate), polyethylene, polypropylene, Lexan andcellulose acetate.

The sheet 20 is movably positioned, i.e., abutted, against the back ofthe sheet 12 before typing begins of the surface 18. After typing iscompleted, the backing sheet is removed, and a thermal transferduplicating process is carried to completion in the conventional manner,as previously described.

Thus, the typed surface of the original is positioned against aconventional thermal transfer sheet substrate carrying a fusible layerof heat sensitive material on the opposite side and an image-receivingsheet is positioned on said opposite side of the heat transfer sheet.Exposure to infrared radiation is then carried out to form a visible,transferred image on the image-receiving sheet. This imaged sheet isthen used as the desired duplicate or as a master for providing thedesired number of duplicate imaged copies, as by the spirit master orother solvent process or the like. The duplicate and copies show a highdegree of resolution, edge sharpness, uniformity and clarity and aresubstantially better than copies provided by conventional thermalduplicating processes or impact transfer processes.

The following specific Examples, in which all parts are by weight,illustrate further features of the invention:

EXAMPLE 1 Thirty parts of a hydrated aluminum silicate, sold by theGeorgia Kaolin Co. under the trademark Hydrite 10, parts of glass beadsaveraging 40 microns in diameter and about 17 parts of an acrylicemulsion, sold by Rohm & Haas Co. under the trademark Rhoplex AC61 aremixed together in about 50 parts water. The Hydrite 10 is oil receptive,having an average particle diameter of about 0.5 microns and 42 weightpercent oil absorption. The glass beads are oil 6 resistive. The RhoplexAC-61 forms a binder for the particles and contains 46 weight percentacrylic solids.

The mixture is coated on tissue paper of about 1.5 mil thickness andcalendered and dried to a thickness of about 0.3 mil to form a sheet oftyping paper. The coated typing paper is then backed by a 5 mil thicksheet of smooth Mylar (polyethylene terephthalate) while inkedcharacters are placed on the typing surface by typing with a standardtypewriter utilizing a conventional inked typing ribbon. The resultingtyped image is found to be of uniform color, density and distributionand to'exhibit character break-up (microscopically) into a. uniformdistribution of small sub-units. The typed original exhibits noappreciable indenting by the typing keys and provides clear, uniform andsharp copies when subjects to a thermal duplication process.

In the duplication process, the typed surface of the original isoverlaid with a conventional thermal transfer sheet, in turn overlaidwith a conventional imagereceiving sheet. The composite is then exposedto infrared radiation to form a thermal image from the image on theoriginal and to form a visible image in the imagereceiving sheet bytransfer from the transfer sheet. This visible image, when compared withthe original image, is found to be of very high quality.

EXAMPLE 2 Fifty-one parts of a calcite clay, sold by the Georgia KaolinCo. under the trademark Glomax HE, 78 parts of Hydrite 10, parts of acalcium carbonate, sold by the Georgia Marble Co. under the designationno. 10 white, 27 parts of a polyvinyl acetate solution, sold by theNational Starch Co. under the trademark Resyn 1105 and 19 parts ofstarch sold under the trademark Cato Kote 485 are mixed together. TheGlomax HE is oil receptive, as is the Hydrite 10, having an averageparticle diameter size of about 1 micron or less and about 65 weightpercent oil absorption. The No. 10 white calcium carbonate is oilresistive, having an average particle diameter of about 10 microns orhigher and about 7-9 weight percent oil absorption. The Resyn 1105 formsa binder for the particles and contains about 4.7 weight percentpolyvinyl acetate solids. The mixture is spread as a wet coating on asubstrate comprising 1.5 mil thick paper and calendered at 1000 p.l.s.with a smooth steel roller to provide a finished dry coating having athickness of 0.3 mil. The coated paper sheet is then backed by a smoothplastic sheet of cellulose acetate about 5.0 mils thick and the coatedsurface is imprinted with inked type characters, as set forth inExample 1. The typed sheet is then processed as in Example 1 to providea duplicate. The duplicate image, when compared with the original image,is found to be very accurate, sharp, uniform and of overall highquality.

What is claimed is:

1. An improved image control means for a thermal duplicating process,comprising, in combination:

an original compliant typing sheet having a thickness of about 1.5-2.5mils, said sheet having a typing surface receptive to typing ink andresistant to ink transfer therefrom, said surface being coated with asubstantially uniform mixture of oil receptive particles having anaverage diameter of less than 4 microns and having an oil absorption ofat least 30 weight percent, and oil resistive particles having anaverage diameter of at least 8 microns and having an oil absorption ofless than 20 weight percent,

7 said particles being selected from the group consisting of inorganicsalt, inorganic oxide and mixtures thereof dispersed in a dry adhesivebinder, the volume ratio of said oil receptive particles to said oilresistive particles being about 0.511 to about 8:1; and

a smooth resilient backing sheet abutted against the back of said typingsheet, said backing sheet having a thickness of about 2-5 mils.

2. The improved control means of claim 1 wherein said typing sheetcomprises paper stock bearing said mixture as a thin calendered coatingthereon.

3. The improved control means of claim 1 wherein said typing sheetcomprises polypropylene plastic.

4. The improved control means of claim 1 wherein said backing sheetcomprises cellulose acetate plastic.

5. An improved typing member comprising a compliant sheet having athickness of about 1.5-2.5 mils, said sheet having a typing surfacereceptive to typing ink and resistant to ink transfer therefrom, saidsurface being coated with a substantially uniform mixture of oilreceptive particles having an average diameter of less than 4 micronsand having an oil absorption of at least 30 weight percent, and oilresistive particles having an average diameter of at least 8 microns andhaving an oil absorption of less than 20 weight percent, said particlesbeing selected from the group consisting of inorganic salt, inorganicoxide and mixtures thereof dispersed in a dry adhesive binder, thevolume ratio of said oil receptive particles to said oil resistiveparticles being about 0.511 to about 8:1.

6. The improved typing member of claim 5 wherein said typing sheetcomprises paper stock bearing said mixture as a thin calendered coatingthereon.

7. In a thermal duplicating process wherein an original typing sheet istyped to provide an image to be duplicated and thereafter a thermalduplicate is prepared from said typed original, the improvement whichcomprises typing on an original compliant typing sheet having athickness of about 1.5-2.5 mils, said sheet having a typing surfacereceptive to typing ink and resistant to ink transfer therefrom, saidsurface being coated with a substantially uniform mixture of oilreceptive and oil resistive particles, said oil receptive particleshaving an average diameter of less than 4 microns and an oil absorptionof at least 30 weight percent and said oil resistive particles having anaverage diameter of at least 8 microns and an oil absorption of lessthan 20 weight percent, said particles being selected from the groupconsisting of inorganic salt, inorganic oxide and mixtures thereofdispersed in a dry adhesive binder the volume ratio of said oilreceptive particles to said oil resistive particles is about 0.5 :l toabout 8:1, said typing being carried out while said typing sheet isbacked by a flexible smooth resilient backing sheet having a thicknessof about 2.0-5 mils and including the step of thereafter removing saidtyping sheet from said backing sheet.

8. The improvement of claim 7 wherein said typing sheet comprises paperstock bearing said mixture as a thin calendered coating as said typingsurface.

1. AN IMPROVEMENT IMAGE CONTROL MEANS FOR A THERMAL DUPLICATING PROCESS,COMPRISING, IN COMBINATION: AN ORGINAL COMPLIANT TYING SHEET HAVING ATHICKNESS OF ABOUT 1.5-2.5 MILS, SAID SHEET HAVING A TYPING SURFACERECEPTIVE TO TYPING INK AND RESISTANT TO INK TRANSFER THEREFROM, SAIDSURFACE BEING COATED WITH A SUBSTANTIALLY UNIFORM MIXTURE OF OILRECEPTIVE PARTICLES HAVING AN AVERAGE DIAMETER OF LESS THAN 4 MICORNSAND HAVING AN OIL ABSORPTION OF AT LEAST 30 WEIGHT PERCENT, AND OILRESISTIVE PARTICLES HAVING AN AVERAGE DIAMETER OF AT LEAST 8 MICRONS AND2. The improved control means of claim 1 wherein said typing sheetcomprises paper stock bearing said mixture as a thin calendered coatingthereon.
 3. The improved control means of claim 1 wherein said typingsheet comprises polypropylene plastic.
 4. The improved control means ofclaim 1 wherein said backing sheet comprises cellulose acetate plastic.5. An improved typing member comprising a compliant sheet having athickness of about 1.5-2.5 mils, said sheet having a typing surfacereceptive to typing ink and resistant to ink transfer therefrom, saidsurface being coated with a substantially uniform mixture of oilreceptive particles having an average diameter of less than 4 micronsand having an oil absorption of at least 30 weight percent, and oilresistive particles having an average diameter of at least 8 microns andhaving an oil absorption of less than 20 weight percent, said particlesbeing selected from the group consisting of inorganic salt, inorganicoxide and mixtures thereoF dispersed in a dry adhesive binder, thevolume ratio of said oil receptive particles to said oil resistiveparticles being about 0.5:1 to about 8:1.
 6. The improved typing memberof claim 5 wherein said typing sheet comprises paper stock bearing saidmixture as a thin calendered coating thereon.
 7. In a thermalduplicating process wherein an original typing sheet is typed to providean image to be duplicated and thereafter a thermal duplicate is preparedfrom said typed original, the improvement which comprises typing on anoriginal compliant typing sheet having a thickness of about 1.5-2.5mils, said sheet having a typing surface receptive to typing ink andresistant to ink transfer therefrom, said surface being coated with asubstantially uniform mixture of oil receptive and oil resistiveparticles, said oil receptive particles having an average diameter ofless than 4 microns and an oil absorption of at least 30 weight percentand said oil resistive particles having an average diameter of at least8 microns and an oil absorption of less than 20 weight percent, saidparticles being selected from the group consisting of inorganic salt,inorganic oxide and mixtures thereof dispersed in a dry adhesive binderthe volume ratio of said oil receptive particles to said oil resistiveparticles is about 0.5:1 to about 8:1, said typing being carried outwhile said typing sheet is backed by a flexible smooth resilient backingsheet having a thickness of about 2.0-5 mils and including the step ofthereafter removing said typing sheet from said backing sheet.
 8. Theimprovement of claim 7 wherein said typing sheet comprises paper stockbearing said mixture as a thin calendered coating as said typingsurface.